Methods for forming a semiconductor device and related semiconductor device structures

ABSTRACT

Methods for forming a semiconductor device and related semiconductor device structures are provided. In some embodiments, methods may include forming an NMOS gate dielectric and a PMOS gate dielectric over a substrate and forming a first work function metal over the NMOS gate dielectric and over the PMOS gate dielectric. In some embodiments, methods may also include, removing the first work function metal over the NMOS gate dielectric and forming a second work function metal over the NMOS gate dielectric and over the PMOS gate dielectric. In some embodiments, related semiconductor device structures may include an NMOS gate dielectric and a PMOS gate dielectric disposed over a semiconductor substrate. A PMOS gate electrode may be disposed over the PMOS gate dielectric and the PMOS gate electrode may include a first work function metal disposed over the PMOS gate dielectric and a second work function metal disposed over the first work function metal. A NMOS gate electrode may be disposed over the NMOS gate dielectric and the NMOS gate electrode may include the second work function metal.

BACKGROUND Field of the Invention

The present disclosure relates generally to methods for forming semiconductor devices and particular to forming CMOS semiconductor devices and related semiconductor device structures.

Description of the Related Art

Metal-oxide-semiconductor (MOS) technology has conventionally utilized n-type and p-type doped polysilicon as the gate electrode material. However, doped polysilicon may not be an ideal gate electrode material for advanced node applications. For example, although doped polysilicon is conductive, there may still be a surface region which can be depleted of carriers under bias conditions. This region may appear as an extra gate insulator thickness, commonly referred to as gate depletion, and may contribute to the equivalent oxide thickness. While the gate depletion region may be thin, on the order of a few angstroms (Å), it may become significant as the gate oxide thicknesses are reduced in advance node applications. As a further example, polysilicon does not exhibit an ideal effective work function (eWF) for both NMOS and PMOS devices. To overcome the non-ideal effective work function of doped polysilicon, a threshold voltage adjustment implantation may be utilized. However, as device geometries reduce in advanced node applications, the threshold voltage adjustment implantation processes may become increasingly complex and impractical.

To overcome the problems associated with doped polysilicon gate electrodes, the non-ideal doped polysilicon gate material may be replaced with alternative materials, such as, for example, a transition metal nitride, a transition metal aluminide or a transition metal carbide. For example, the properties of a transition metal nitride, a transition metal aluminide or a transition metal carbide may be utilized to provide a more ideal effective work function for NMOS and PMOS devices, where the effective work function of the gate electrode, i.e., the energy needed to extract an electron, may be compatible with the barrier height of the semiconductor material. For example, in the case of PMOS devices, the effective work function is approximately 5.0-5.2 eV and in the case of NMOS devices, the effective work function is approximately 4.1-4.3 eV.

SUMMARY

This summary is provided to introduce a selection of concepts in a simplified form. These concepts are described in further detail in the detailed description of example embodiments of the disclosure below. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

In some embodiments, methods for forming a semiconductor device are provided. The methods may comprise forming an NMOS gate dielectric and a PMOS gate dielectric over a semiconductor substrate and forming a first work function metal over the NMOS gate dielectric and over the PMOS gate dielectric. The methods may also include removing the first work function metal over the NMOS gate dielectric and forming a second work function metal over the NMOS gate dielectric and over the PMOS dielectric.

In some embodiments, methods for forming a CMOS semiconductor device are provided. The methods may comprise, forming an NMOS gate dielectric and a PMOS gate dielectric over a semiconductor substrate and depositing by atomic layer deposition a niobium nitride layer over the NMOS gate dielectric and over the PMOS gate dielectric. The methods may also include, etching the niobium nitride layer over the NMOS gate dielectric and depositing by atomic layer deposition at least one of a transition metal aluminide and a transition metal carbide over the NMOS gate dielectric and over the PMOS gate dielectric.

In some embodiments, a semiconductor device structure is provide. The semiconductor device structure may include an NMOS gate dielectric and a PMOS gate dielectric disposed over a semiconductor substrate. The semiconductor device structure may also include a PMOS gate electrode disposed over the PMOS gate dielectric, the PMOS gate electrode including a first work function metal disposed over the PMOS gate dielectric and a second work function metal disposed over the first work function metal. The semiconductor device structure may also include an NMOS gate electrode disposed over the NMOS gate dielectric, the NMOS gate dielectric comprising the second work function metal.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing out and distinctly claiming what are regarded as embodiments of the invention, the advantages of embodiments of the disclosure may be more readily ascertained from the description of certain examples of embodiments of the disclosure when read in conjunction with the accompanying drawings, in which:

FIGS. 1-13 are simplified cross section views of semiconductor device structures formed according to the embodiments of the disclosure;

FIG. 14 is a graph showing the effective work function (eWF) of various effective work function metals as a function of film thickness.

DETAILED DESCRIPTION

The illustrations presented herein are not meant to be actual view of any particular material, structure, or device, but are merely idealized representations that are used to describe embodiments of the disclosure.

As used herein, the term “atomic layer deposition” (ALD) may refer to a vapor deposition process in which deposition cycles, in some instances a plurality of consecutive deposition cycles, are conducted in a process chamber. Typically, during each cycle the precursor is chemisorbed to a deposition surface (e.g., a substrate surface or a previously deposited underlying surface such as material from a previous ALD cycle), forming a monolayer or sub-monolayer that does not readily react with additional precursor (i.e., a self-limiting reaction). Thereafter, if necessary, a reactant (e.g., another precursor or reaction gas) may subsequently be introduced into the process chamber for use in converting the chemisorbed precursor to the desired material on the deposition surface. Typically, this reactant is capable of further reaction with the precursor. Further, purging steps may also be utilized during each cycle to remove excess precursor from the process chamber and/or remove excess reactant and/or reaction byproducts from the process chamber after conversion of the chemisorbed precursor. Further, the term “atomic layer deposition,” as used herein, is also meant to include processes designated by related terms such as, “chemical vapor atomic layer deposition”, “atomic layer epitaxy” (ALE), molecular beam epitaxy (MBE), gas source MBE, or organometallic MBE, and chemical beam epitaxy when performed with alternating pulses of precursor composition(s), reactive gas, and purge (e.g., inert carrier) gas.

As used herein, the term “substrate” may refer to any underlying material or materials that may be used, or upon which a device, a circuit or a film may be formed.

As used herein, the term “alkyl-hydrazine” may refer to a derivative of hydrazine (N₂H₄) which may comprise an alkyl functional group and may also comprise additional functional groups.

As used herein, the term “work function metal” may refer to any conductive metal-containing material that results in an appropriate work function when formed in, on or over the gate dielectric of a gate electrode.

The present disclosure includes methods and semiconductor device structures that may be used to form gate electrodes comprising one or more work function metals, wherein the work function metals may be formed utilizing an atomic layer deposition process. The existing work function metals that may be utilized in the ALD formation of gate electrodes may have limitations due to their unsuitable effective work function values. For example, it is known that the effective work function of a material may vary as a function of its thickness. Therefore, as device geometries decrease in advanced node applications, the thickness of the corresponding device films, such as the work function metal(s) of the gate electrode, may also decrease in thickness with an associated change in the effective work function. Such a change in the effective work function of the gate electrode at reduced work function metal thickness may result in a non-ideal effective work function for NMOS and PMOS device structures. Methods and structures are therefore required to provide a more desirable gate electrode. Examples of such methods and structures are disclosed in further detail below. Atomic layer deposition (ALD) may be utilized for the deposition of transition metal nitride films, transition metal aluminide films and transition metal carbide films, such as, for example, titanium aluminide (TiAl), tantalum nitride (TaN), titanium nitride (TiN), tungsten nitride (WN), niobium nitride (NbN), niobium titanium nitride (NbTiN), titanium-aluminum carbide (TiAlC) and niobium-aluminum carbide (NbAlC). However, the known methods and structures for utilizing such transition metal films for gate electrode purposes may be unsatisfactory for CMOS device fabrication.

The following embodiments of the disclosure may be illustrated using a non-limiting example CMOS process flow commonly referred to in the art as “gate last”, wherein the gate electrode may be formed after source/drain region formation and associated high temperature activation processes. It should however be understood that the “gate last” embodiments illustrated in the current disclosure are non-limiting example embodiments of processes that may be utilized in the formation of example CMOS device structures including NMOS and PMOS device structures. The methods and semiconductor device structures of the embodiments of the disclosure described herein may also be utilized in alternative CMOS process flows. Such an alternative CMOS process flow may include a CMOS process flow commonly referred to in the art as “gate first”, wherein the gate electrode may be formed prior to source/drain region formation and associated high temperature activation processes. Common CMOS process flows are described in U.S. Pat. No. 9,136,180, issued to Machkaoutsan, et al., and incorporated by reference herein.

It should be noted that the various embodiments of methods and semiconductor device structures described herein include various steps in the design and composition of the semiconductor device structures that are well known and so, in the interest of brevity, many conventional steps and structures have only been mentioned briefly herein or omitted entirely. In addition, a number of example materials are given throughout the embodiments of the current disclosure, it should be noted that the chemical formulas given for each of the example materials should not be construed as limiting and that the non-limiting example materials given should not be limited by a given example stoichiometry.

In some embodiments, methods of the disclosure may comprise forming an NMOS gate dielectric and a PMOS gate dielectric over a semiconductor substrate and forming a first work function metal over the NMOS gate dielectric and over the PMOS gate dielectric. Embodiments may also include, removing the first work function metal over the NMOS gate dielectric and forming a second work function metal over the NMOS gate dielectric and over the PMOS gate dielectric.

In more detail and with reference to FIG. 1, a semiconductor device structure 100 may comprise a semiconductor substrate 102 and sacrificial gate structures 104 formed over a surface 106 of the semiconductor substrate 102. The semiconductor substrate 102 may further comprise a PMOS region 108 and an NMOS region 110 wherein the PMOS and NMOS source/drain and channel regions may be subsequently formed. For the purpose of simplicity in describing the embodiments of the disclosure, only a single PMOS region 108 and a single NMOS region 110 are shown but it should be appreciated that the methods and structures disclosed herein also apply to semiconductor device structures including a high number of PMOS regions and NMOS regions. The semiconductor substrate 102 may also comprise a shallow trench isolation (STI) 112, wherein the STI 112 separates and delineates the PMOS region 108 and the NMOS region 110.

The semiconductor substrate 102 may comprise, for example, a bulk silicon substrate or a silicon-on-insulator (SOI) substrate, wherein the SOI substrate further includes a support substrate and an intermediate buried oxide layer (not shown). In some embodiments, the semiconductor substrate 102 may comprise at least one of silicon germanium, germanium, silicon carbide or a III-V material. In some embodiments, the semiconductor substrate 102 may be in the form of a fin structure for use in a FinFET type device, whereas in FIG. 1 semiconductor substrate 102 comprises a substantially planar surface 106.

As illustrate in FIG. 1, sacrificial gate structures 104 may be formed over the surface 106 of semiconductor substrate 102. In some embodiments, the sacrificial gate structures 104 may comprise a sacrificial gate 114 and a sacrificial cap 116, wherein the sacrificial cap may be formed directly over the sacrificial gate 114. The sacrificial gate structures 104 may be formed using conventional processes steps such as deposition, photolithography, and etching. The sacrificial gates 114 may comprise a polycrystalline silicon material and the sacrificial cap 116 may comprise a silicon oxide or a silicon nitride.

After sacrificial gate structure formation, spacers may be formed on either side of the sacrificial gate structures as illustrate in FIG. 2. In more detail, FIG. 2 illustrates semiconductor device structure 118 which comprises spacers 120. The spacers 120 may be formed adjacent to and on the sides of the sacrificial gate structures 104. In some embodiments, the spacers 120 may comprise a silicon nitride material and may be formed by an ALD process.

Upon spacer formation, processes for formation of source/drain regions in the semiconductor substrate 102 may be performed, including, but not limited to, etching, epitaxial deposition, stressing techniques, and ion implantation using the sacrificial gate structures as ion implantation masks. Processes for formation of source/drain regions in the semiconductor substrate 102 may result in the formation of PMOS region 108 and NMOS region 110 in semiconductor substrate 102 (details of source/drain and channel regions are not shown for simplicity).

Embodiments of the disclosure may continue with the formation of an interlayer dielectric (ILD) comprising a dielectric material surrounding the spacers. FIG. 3 illustrates semiconductor device structure 122 comprising dielectric material 124. The dielectric material 124 may be formed utilizing deposition techniques, such as, chemical vapor deposition (CVD), low pressure chemical vapor deposition (LPCVD) or plasma enhanced chemical vapor deposition (PECVD). The dielectric material 124 may be deposited such that it fills the areas between the spacers 120 and covers the spacers 120 and the sacrificial caps 116. The dielectric material 124 may be subsequently planarized, for example, utilizing a chemical mechanical polishing process to provide a planar surface, the sacrificial caps 116 serving as a polish stop indicator.

Upon deposition of the ILD, embodiments of the disclosure may continue by removing the sacrificial gate structures. For example, FIG. 4 illustrates semiconductor device structure 126 which shows the semiconductor device structure 122 of FIG. 3 after removal of the sacrificial gate structures, whilst leaving the spacers 120 substantially intact. The removal of the sacrificial gate structures may expose surface 106 in the regions between the spacers 120. Removing the sacrificial gate structures comprises the formation of the gate trenches 128, the gate trenches 128 being bounded by spacers 120 and surface 106. The sacrificial gate structures are removed by an etching process, the etch chemistry being selected such that the spacers 120 and the dielectric material 124 are not etched, or are not etched significantly. The sacrificial gate structures may be removed by a dry etch process, a wet etch process or a combination thereof.

The embodiments of the disclosure may continue with the formation of an interface layer in the gate trenches. As illustrated in FIG. 5, a semiconductor device structure 130 may include an interface layer 132 that may be formed on the surface 106 of semiconductor substrate 102 disposed in the gate trenches 128. In some embodiments, the interface layer 132 may comprise a silicon oxide and may be selectively formed on the surface 106 utilizing a chemical oxidation process to oxidize the surface 106 of semiconductor substrate 102. In some embodiment, methods may comprise forming the interface layer 132 to a thickness of approximately less than 1 nm. In some embodiments, the interface layer 132 may be disposed over the channel region of the NMOS region 110 and over the channel region of the PMOS region 108.

The embodiments of the disclosure may further comprise forming a gate dielectric. As a non-limiting example embodiment, a conformal layer of high-k dielectric material may be formed over the semiconductor device structure 130 of FIG. 5, resulting in semiconductor device structure 134 as illustrated in FIG. 6. For example, the high-k dielectric material 136 disposed over the NMOS region 110 may be denoted as NMOS dielectric 136A and the high-k dielectric material 136 disposed over the PMOS region 108 may be denoted as PMOS dielectric 136B. In some embodiments therefore, forming the NMOS gate dielectric 136A and the PMOS gate dielectric 136B may comprise depositing a high-k dielectric material 136 directly over the interface layer 132.

In some embodiments, the high-k dielectric material 136 may comprise at least one of hafnium oxide (HfO₂), tantalum oxide (Ta₂O₅), zirconium oxide (ZrO₂), titanium oxide (TiO₂), hafnium silicate (HfSiO_(x)) and lanthanum oxide (La₂O₃). In some embodiments, the high-k dielectric material 136 may comprise at least one of dielectric metal oxide, such as transition metal oxide or aluminum oxide, metal silicates, dielectric metal oxynitride or mixtures thereof. In some embodiments of the disclosure, the high-k dielectric material 136 may be conformally deposited using an atomic layer deposition process. In some embodiments, methods may comprise forming the high-k dielectric material 136 to have a thickness of approximately less than 2 nm.

Embodiments of the disclosure may further comprise forming a first work function metal over the NMOS gate dielectric and the PMOS gate dielectric. As illustrated in FIG. 7, a semiconductor 138 may comprise a first metal work function 140 that may be formed conformally over the NMOS gate dielectric 136A and the PMOS gate dielectric 136B. Embodiments of the disclosure may further comprise selecting the first work function metal 140 to comprise a p-type work function metal which may include a niobium nitride. For example, in some embodiments the first work function metal 140 may comprise a niobium nitride wherein the niobium nitride may comprise NbN. In some embodiments, the first work function metal may comprise a niobium nitride wherein the niobium nitride may comprise some other metal or metal nitride, such as a transition metal or a transition metal nitride, such as a niobium titanium nitride (NbTiN). In some embodiments, the first work function may metal may comprise TiN_(x)/Ti or TaN_(x)/Ta. In other embodiments, the first work function metal, e.g., a niobium nitride, may be formed by a deposition process and in further embodiments, the deposition process may comprise a cyclical deposition process, such as an atomic layer deposition process, as disclosed in more detail herein below, or a cyclical CVD process.

ALD is based on typically self-limiting reactions, whereby sequential and alternating pulses of reactants are used to deposit about one atomic (or molecular) monolayer of material per deposition cycle. The deposition conditions and precursors are typically selected to provide self-saturating reactions, such that an adsorbed layer of one reactant leaves a surface termination that is non-reactive with the gas phase reactants of the same reactant. The substrate is subsequently contacted with a different reactant that reacts with the previous termination to enable continued deposition. Thus, each cycle of alternated pulses typically leaves no more than about one monolayer of the desired material. However, as mentioned above, the skilled artisan will recognize that in one or more ALD cycles more than one monolayer of material may be deposited, for example if some gas phase reactions occur despite the alternating nature of the process.

In an ALD-type process for depositing transition metal nitride films, such as a niobium nitride, one deposition cycle comprises exposing the substrate to a first reactant, removing any unreacted first reactant and reaction byproducts from the reaction space, exposing the substrate to a second reactant, followed by a second removal step. The first vapor phase reactant may comprise a metal precursor, in particular a transition metal precursor, such as a niobium precursor. The second reactant may comprise a nitrogen precursor,

In some non-limiting example embodiments, the first vapor phase reactant may comprise a niobium vapor phase reactant, such as niobium halide, which may comprise at least one of niobium pentafluoride (NbF₅), niobium pentaiodide (NbI₅), niobium pentachloride (NbCl₅) and niobium pentabromide (NbBr₅). In some non-limiting example embodiments, the first vapor phase reactant may comprise a metal-organic or organometallic niobium vapor phase reactant, such as niobium alkylamine precursor.

In some non-limiting example embodiments, the second vapor phase reactant may comprise a nitrogen containing reactant comprising at least one of ammonia (NH₃), hydrazine (N₂H₄) and an alkyl-hydrazine precursor. In embodiments in which the nitrogen containing reactant comprises an alkyl-hydrazine precursor, the alkyl-hydrazine precursor may comprise at least one of tertbutylhydrazine (C₄H₉N₂H₃), methylhydrazine (CH₃NHNH₂), dimethylhydrazine ((CH₃)₂N₂H₂). In embodiments in which the nitrogen containing reactant comprises an alkyl-hydrazine precursor, the alkyl group might be C1-C4 linear or branched alkyl group, such as Me, Et, ^(n)Pr, ^(i)Pr, ^(n)Bu, ^(i)Bu or ^(t)Bu. In some embodiments the second vapor phase reactant may comprise nitrogen radicals, atomic nitrogen or plasma comprising nitrogen. In some embodiments the second vapor phase reactant may also comprise only or in addition to nitrogen species, hydrogen radicals, atomic hydrogen or plasma comprising hydrogen. In some embodiments the second vapor phase reactant may comprise excited species of nitrogen and/or hydrogen. In some embodiments the second vapor phase reactant comprising excited species, plasma, radicals or atomic nitrogen and/or hydrogen may be formed from NH₃ N₂/H₂ mixture or from N₂H₄.

Precursors may be separated by inert gases, such as argon (Ar) or nitrogen (N₂), to prevent gas-phase reactions between reactants and enable self-saturating surface reactions. In some embodiments, however, the substrate may be moved to separately contact a first metal reactant and a second nitrogen reactant. Because the reactions self-saturate, strict temperature control of the substrates and precise dosage control of the precursors is not usually required. However, the substrate temperature may be such that an incident gas species does not condense into monolayers nor decompose on the surface. Surplus chemicals and reaction byproducts, if any, are removed from the substrate surface, such as by purging the reaction space or by moving the substrate, before the substrate is contacted with the next reactive chemical. Undesired gaseous molecules can be effectively expelled from a reaction space with the help of an inert purging gas. A vacuum pump may be used to assist in the purging.

According to some embodiments, ALD-type processes are used to form a first work function metal, for example, a niobium nitride over an NMOS gate dielectric and over a PMOS gate dielectric. Each ALD cycle may comprise two distinct deposition steps or phases. In a first phase of the deposition cycle (“the metal phase”), the substrate surface on which deposition is desired is contacted with a first reactant comprising a transition metal such as niobium (i.e., niobium source material or chemical) which chemisorbs onto the substrate surface, forming no more than about one monolayer of reactant species on the surface of the substrate.

In some embodiments, the transition metal (e.g., niobium) source chemical, also referred to herein as the “transition metal compound” (or in some embodiments as the “niobium compound”), is a halide and the adsorbed monolayer is terminated with halogen ligands. In some embodiments, the niobium halide may be at least one of niobium pentachloride (NbCl₅) and niobium pentafluoride (NbF₅).

Excess transition metal (e.g., niobium) source material and reaction byproducts (if any) may be removed from the substrate surface, e.g., by purging with an inert gas. Excess transition metal source material and any reaction byproducts may be removed with the aid of a vacuum generated by a pumping system.

In a second phase of the deposition cycle (“the nitrogen phase”), the substrate is contacted with at least one of ammonia, hydrazine and an alkyl-hydrazine. In some embodiments the alkyl-hydrazine may comprise at least one of tertbutylhydrazine, methylhydrazine and dimethylhydrazine. The second nitrogen reactant may react with the niobium-containing molecules left on the substrate surface. In the second phase nitrogen is incorporated into the film by the interaction of the nitrogen reactant with the monolayer left by the transition metal (e.g., niobium) source material. In some embodiments, reaction between the nitrogen reactant and the chemisorbed transition metal species produces a transition metal nitride thin film over the substrate and particular a niobium nitride over the NMOS gate dielectric and over the PMOS gate dielectric.

Excess second source chemical and reaction byproducts, if any, are removed from the substrate surface, for example by a purging gas pulse and/or vacuum generated by a pumping system. Purging gas is may comprise any inert gas, such as, without limitation, argon (Ar), nitrogen (N₂) or helium (He). A phase is generally considered to immediately follow another phase if a purge (i.e., purging gas pulse) or other reactant removal step intervenes.

In some embodiments, the niobium nitride may comprise a niobium titanium nitride and the niobium titanium nitride may be formed by an ALD processes. As a non-limiting example embodiment, the process for atomic layer deposition of niobium titanium nitride may comprise a plurality of deposition cycles, each deposition cycle having a NbN sub-cycle and TiN sub-cycle.

The NbN sub-cycle may include alternately and sequentially contacting the substrate with a niobium vapor phase reactant (as described herein) and a nitrogen containing reactant (as described herein). The NbN formed by the embodiments of the disclosure may take the form NbN_(x) wherein x may range from approximately 0.75 to approximately 1.8, or wherein x may range from approximately 0.8 to approximately 1.5, or wherein x may range from 0.9 to approximately 1.3, or alternatively wherein x may range from approximately 0.95 to approximately 1.2. The elemental composition ranges for NbN_(x) (excluding other metal or metal nitride mixed such as TiN) may comprise Nb from about 30 atomic % to about 60 atomic %, or from about 35 atomic % to about 55 atomic %, or even from about 40 atomic % to about 50 atomic %. Alternatively the elemental composition ranges for NbN_(x) may comprise N from about 25 atomic % to about 65 atomic %, or N from about 30 atomic % to about 60 atomic %, or even N from about 35 atomic % to about 55 atomic %. In additional embodiments the NbN may comprise less than about 20 atomic % oxygen, less than about 10 atomic % oxygen, less than about 5 atomic % oxygen, or even less than about 2 atomic % oxygen. In further embodiments, the NbN may comprise less than about 30 atomic % hydrogen, or less than about 15 atomic % of hydrogen, or less than about 10 atomic % of hydrogen, or even less than about 5 atomic % of hydrogen. In some embodiments, the NbN may comprise Halide/Cl less than about 10 atomic %, or Halide/Cl less than about 5 atomic %, Halide/Cl less than about 1 atomic %, or even Halide/Cl less than about 0.5 atomic %. In yet further embodiments, the NbN may comprise less than about 20 atomic % carbon, or less than about 10 atomic % carbon, or less than about 5 atomic % carbon, or less than about 1 atomic % of carbon, or even less than about 0.5 atomic % carbon. In some embodiments, the niobium titanium nitride formed by the methods of the embodiments, may comprise greater than 40 atomic % of titanium, or greater than 30 atomic % of titanium or even greater than 20 atomic % of titanium.

The TiN sub-cycle may include alternately and sequentially contacting the substrate with a titanium vapor phase reactant and a nitrogen containing reactant (as described herein). In some embodiments the titanium vapor phase reactant may comprise a titanium halide and may comprise at least one of titanium tetrachloride (TiCl₄), titanium tetraiodide (TiI₄), titanium tetrabromide (TiBr₄), titanium tetrafluoride (TiF₄). In some non-limiting example embodiments, the titanium vapor phase reactant may comprise a metal-organic or organometallic titanium vapor phase reactant, such as titanium alkylamine precursor.

In some embodiments, the ALD process for depositing niobium titanium nitride may comprise a number of cycles, where each cycle may include a number of NbN sub-cycles and a number of TiN sub-cycles. The ratio of the number of NbN sub-cycles to the number of TiN sub-cycles, in a cycle, may be selected to provide a niobium titanium nitride material with desired properties. For example, the ratio of the number of NbN sub-cycles to the number of TiN sub-cycles may be selected to provide a niobium titanium nitride with a desired effective work function.

In some embodiments, the ALD process for depositing niobium titanium nitride may deposit a nanolaminate film comprising multiple NbN and TiN films. In other embodiments, the ALD process for deposit niobium titanium nitride may deposit a non-nanolaminate film, that is, separate and distinct layers may not be visible within the niobium titanium nitride material. For example, a continuous or substantially continuous niobium titanium nitride film may be formed.

In some embodiments of the disclosure, forming the niobium nitride film may comprise forming the niobium nitride film to a thickness of between approximately 1 nm to approximately 5 nm. In some embodiments of the disclosure, forming the niobium nitride film may comprise forming the niobium nitride film to have an electrical resistivity of less than 1000 μΩ-cm, or less than 900 μΩ-cm or even less than 800 μΩ-cm. In further embodiments, forming the first work function metal 140, e.g., a niobium nitride, over the NMOS gate dielectric 136A and the PMOS gate dielectric 136B further comprise depositing the first work metal 140 directly over the NMOS gate dielectric 136A and directly over the PMOS gate dielectric 136B. In yet further embodiments, forming the first work function metal 140, e.g., a niobium nitride, over the NMOS gate dielectric 136A and the PMOS gate dielectric 136B further comprise depositing the first work functional metal 140 directly over the high-k material 136.

The ALD processes described herein, utilizing a niobium precursor and a nitrogen precursor, may be performed in an ALD deposition system with a heated substrate. For example, in some embodiments, methods may comprise heating the substrate to a deposition temperature of between approximately 100° C. and approximately 800° C., or between approximately 150° C. and approximately 650° C., or between approximately 200° C. to approximately 600° C., or between approximately 250° C. to approximately 500° C. or even between approximately 300° C. to approximately 475° C.

The deposition rate of the transition metal nitride film by ALD, which is typically presented as Å/pulsing cycle, depends on a number of factors including, for example, on the number of available reactive surface sites or active sites on the surface and bulkiness of the chemisorbing molecules. In some embodiments, the deposition rate of such films may range from about 0.01 to about 5.0 Å/pulsing cycle, or from about 0.05 to about 2.5 Å/pulsing cycle, or from about 0.1 to about 2.0 Å/pulsing cycle, or even from about 0.15 to about 1.0 Å/pulsing cycle. In some embodiments, the deposition rate can be about 0.1, 0.2, 0.3, 0.5, 1.0, 2.5, 5.0.

The embodiments of the disclosure may continue with the formation of a masking layer over select portions of the first work function metal, wherein the masking layer defines the areas of the first work function metal to remain after a subsequent removal process. For example, FIG. 8 illustrate semiconductor device structure 142 which comprises a masking layer 144 which may be disposed over select portions of the first work function metal 140. The masking layer 144 may be formed and patterned using common semiconductor processes such as spin-coating, deposition, photolithography, development and etching. In some embodiments, the methods of the disclosure may comprise selecting the masking layer 144 to comprise one of a silicon nitride, a silicon oxide or a polymer material (e.g., a photoresist). The masking layer 144 may be disposed over the portions of the first work function metal 140 that may remain after a subsequent removal process, i.e., the masking layer 144 may be disposed over the PMOS gate dielectric 136B.

Embodiments of the disclosure may further comprise, removing the first work function metal over the NMOS gate dielectric. In more detail, FIG. 9 illustrates semiconductor device structure 146 which comprises the first work function metal 140 after removing a portion of the first work function metal 140, in addition to removing the masking layer. Removing the first work function metal over the NMOS gate dielectric 136A may comprise selectively etching the first work function metal 140, wherein the term “selectively etching” may refer to an etching process in which a first material is etched at a significantly higher etching rate than a second material. For example, a ratio of the etching rates between the a first material, e.g., the first work function metal 140, and a second material, e.g., the underlying high-k dielectric 136, may comprise an etching ratio greater than 3:1, 5:1, or even 10:1 or even greater. In some embodiments the first work function metal 140 may comprise a niobium nitride and the niobium nitride may be selectively etched in relation to the underlying high-k dielectric material 136.

In some embodiments, selectively etching the first work function metal 140, e.g., a niobium nitride, further comprises, exposing the first work function metal to at least one of a fluoride-based etch chemistry or a chloride-based etch chemistry. As a non-limiting example, the first work function metal 140 may be exposed to a radical or plasma etch chemistry comprising at least one of sulfur hexafluoride (SF₆), carbon tetrafluoride (CF₄) and nitrogen trifluoride (NF₃). In further embodiments of the disclosure, the etching the first work function metal 140 may comprise one or more of a polishing, grinding or chemical mechanical polishing removal process. As illustrated in FIG. 9 the removal process results in a first work function metal 140 disposed directly over the PMOS gate dielectric 136B.

Embodiments of the disclosure may further comprise forming a second work function metal over the NMOS gate dielectric and over the PMOS gate dielectric. As illustrated in FIG. 10, semiconductor device structure 148 may include a second metal work function 150 that may be formed conformally over the NMOS gate dielectric 136A and over the PMOS gate dielectric 136B. Embodiments of the disclosure may further comprise selecting the second work function metal 150 to comprise an n-type work function metal, such as, for example, an n-type work function metal comprising a transition metal aluminide or an n-type work function metal comprising a transition metal carbide. In some embodiments, the n-type work function metal comprising a transition metal aluminide may include titanium aluminide (TiAl_(x)), zirconium aluminide (ZrAl_(x)), tungsten aluminide (WAl_(x)), tantalum aluminide (TaAl_(x)), and hafnium aluminide (HfAl_(x)). In some embodiments, the n-type work function metal comprising a transition metal carbide may include at least one of a tantalum carbide (TaC_(y)), titanium carbide (TiC_(y)), titanium-aluminum carbide (TiAl_(x)C_(y)) and a niobium-aluminum carbide (NbAl_(x)C_(y)). In some embodiments, the n-type work function metal comprising a transition metal aluminide may further comprise carbon and/or small amounts of impurities. In some embodiments, the second work function metal 150 may be formed by a deposition process and in further embodiments, the deposition process may comprise an atomic layer deposition process, as disclosed in more detail herein below.

In an ALD-type process for depositing a transition metal carbide films, such as a titanium-aluminum carbide (TiAl_(x)C_(y)) and a niobium-aluminum carbide (NbAl_(x)C_(y)), one deposition cycle comprises exposing the substrate to a first reactant, removing any unreacted first reactant and reaction byproducts from the reaction space, exposing the substrate to a second reactant, followed by a second removal step. The first vapor phase reactant may comprise a metal precursor, in particular a transition metal precursor, such as a titanium or a niobium precursor. The second reactant may comprise a carbon and a second metal precursor.

In some non-limiting example embodiments, the first vapor phase reactant may comprise a niobium vapor phase reactant which may comprise at least one of niobium pentachloride (NbCl₅), and niobium pentafluoride (NbF₅), niobium pentaiodide (NbI₅) and niobium pentabromide (NbBr₅). In other non-limiting example embodiments, the first vapor phase reactant may comprise a titanium vapor phase reactant which may comprise at least one of titanium tetrachloride (TiCl₄), titanium tetraiodide (TiI₄), titanium tetrabromide (TiBr₄) and titanium tetrafluoride (TiF₄).

In some non-limiting example embodiments, the second vapor phase reactant may comprise a carbon containing reactant as well as a second metal reactant, such as alkylaluminum compound, and may comprising at least one of trimethylaluminum (TMA), triethylaluminum (TEA), dimethylaluminumhydride (DMAH) and tris(tertbutyl)aluminum (TTBA).

According to some embodiments, ALD-type processes are used to form a second work function metal, over an NMOS gate dielectric and a PMOS gate dielectric. Each ALD cycle may comprise two distinct deposition steps or phases. In a first phase of the deposition cycle (“the metal phase”), the substrate surface on which deposition is desired is contacted with a first reactant comprising a transition metal such as titanium or niobium (i.e., titanium or niobium source material or chemical) which chemisorbs onto the substrate surface, forming no more than about one monolayer of reactant species on the surface of the substrate.

In some embodiments, the transition metal (e.g., titanium or niobium) source chemical, also referred to herein as the “transition metal compound” (or in some embodiments as the “titanium compound” or “niobium compound”), is a halide and the adsorbed monolayer is terminated with halogen ligands.

Excess transition metal (e.g., titanium or niobium) source material and reaction byproducts (if any) may be removed from the substrate surface, e.g., by purging with an inert gas. Excess transition metal source material and any reaction byproducts may be removed with the aid of a vacuum generated by a pumping system.

In a second phase of the deposition cycle (“the carbon phase”), the substrate is contacted with at least one of trimethylaluminum, triethylaluminum, dimethylaluminumhydride (DMAH) and tris(tertbutyl)aluminum (TTBA). The second carbon reactant may react with the transition metal-containing molecules left on the substrate surface. In the second phase carbon and a second metal, such as aluminum, are incorporated into the film by the interaction of the carbon reactant with the monolayer left by the transition metal source material. In some embodiments, reaction between the carbon reactant and the chemisorbed transition metal species produces a transition metal carbide thin film over the substrate and particular at least one of titanium-aluminum carbide and niobium-aluminum carbide over the NMOS gate dielectric and over the PMOS gate dielectric.

Excess second source chemical and reaction byproducts, if any, are removed from the substrate surface, for example by a purging gas pulse and/or vacuum generated by a pumping system. Purging gas is in some embodiments any inert gas, such as, without limitation, argon (Ar), nitrogen (N₂), or helium (He). A phase is generally considered to immediately follow another phase if a purge (i.e., purging gas pulse) or other reactant removal step intervenes.

In an ALD-type process for depositing a transition metal aluminide film, such as a titanium aluminide, one deposition cycle comprises exposing the substrate to a first reactant, removing any unreacted first reactant and reaction byproducts from the reaction space, exposing the substrate to a second reactant, followed by a second removal step. The first vapor phase reactant may comprise a metal precursor, in particular a transition metal precursor, such as a titanium precursor. The second reactant may comprise an aluminum metal precursor.

In some embodiments of the disclosure, forming the second work function metal 150 may comprise forming the second work function metal 150 to a thickness of between approximately 1 nm to approximately 5 nm. In further embodiments, forming the second work function metal 150 over the NMOS gate dielectric and the PMOS gate dielectric further comprise depositing the second work functional metal 150 directly over the NMOS gate dielectric 136A. In additional embodiments, the methods may further comprise depositing the second work function metal 150 directly over the first work function metal 140, wherein the first work function metal 140 is disposed over the PMOS gate dielectric 136B.

In some embodiments, depositing the second work function metal 150 directly over the first work function metal 140 forms an effective work function metal over the PMOS gate dielectric 136B. The effective work function metal, comprising the first work function metal and the second work function metal may have an effective work function which may depend on the thickness of the first work function metal and the thickness of the second work function metal, as well as the materials comprising the first work function metal and the second work function metal.

FIG. 14 is a graph showing the effective work function (eWF) of two example effective work function metals compared to a reference titanium nitride film. The eWF line labelled as 166 indicates the reference eWF of a titanium nitride film formed by ALD, with a 5 nm titanium aluminum carbide layer on top, as a function of the thickness of the titanium nitride layer. The eWF line labelled as 168 indicates the eWF of an effective work function metal comprising niobium nitride and titanium aluminum carbide as a function of niobium nitride thickness (for a fixed titanium aluminum carbide thickness of 5 nm) For the example illustrated by eWF 168 the niobium nitride layer was deposited utilizing an hydrazine precursor. The eWF line labelled as 170 indicates the eWF of an effective work function metal comprising niobium nitride and titanium aluminum carbide as a function of niobium nitride thickness (for a fixed titanium aluminum carbide thickness of 5 nm) For the example illustrated by eWF 170 the niobium nitride layer was deposited utilizing an ammonia precursor. As shown in FIG. 14, the effective work function metals formed by the ALD processes of the current disclosure (i.e., eWF lines 168 and 170) show a marked increase in eWF at reduced film thickness over the reference titanium nitride film 166. For example, at a film thickness of approximately equal to 2 nm (20 Angstroms) the effective work function metals formed utilizing the embodiments of the disclosure show an increase in eWF of greater than 200 meV, or greater than 400 meV, over the reference titanium nitride film.

Therefore, in some embodiments, the effective work function metal may comprise a first work function metal with a thickness of less than or equal to 2 nm and a second work function metal with a thickness of less than or equal to 5 nm with an effective work function of greater than 4.4 eV, or greater than 4.5 eV or even greater than 4.6 eV.

The ALD processes described herein for depositing the second work function metal may be performed in an ALD deposition system with a heated substrate. For example, in some embodiments, methods may comprise heating the substrate to a deposition temperature of between approximately 250° C. and approximately 550° C.

The deposition rate of the second work function metal by ALD, which is typically presented as Å/pulsing cycle, depends on a number of factors including, for example, on the number of available reactive surface sites or active sites on the surface and bulkiness of the chemisorbing molecules. In some embodiments, the deposition rate of such films may range from about 0.1 to about 1.0 Å/pulsing cycle. In some embodiments, the deposition rate can be about 0.1, 0.2, 0.3, 0.5, 1.0 Å/pulsing cycle.

Upon the deposition of the second work function metal, methods of the embodiments may continue by filling the remaining area within the gate trenches with at least one metal fill layer. For example, with reference to FIG. 11, a semiconductor device structure 152 may comprise a liner material 154. In some embodiments, the liner material 154 may be formed over the second work function metal 150. The liner material 154 may be deposited in a conformal manner and in some embodiments the liner material 154 may comprise titanium nitride (TiN). A metal fill material may be deposited over the liner material 154 to complete the sealing of the gate trench as illustrate by semiconductor device structure 156 in FIG. 12. In some embodiments, the metal fill material 158 may comprise tungsten and may be deposited to at least fill the gate trench. Subsequent processes in the embodiments of the disclosure may selectively remove etch excess material from semiconductor device structure 156 of FIG. 12. As illustrated by semiconductor device structure 160 in FIG. 13, one or more etching and/or polishing processes may be utilized to form the planarized semiconductor device structure 160 of FIG. 13.

Upon formation of semiconductor device structure 160 of FIG. 13, further processing may be performed to complete the semiconductor device structure, e.g., to complete a CMOS device structure. For example, back-end-of-line processing may form contacts to the gate electrodes and to source/drain regions as well forming interconnects between devices on the semiconductor substrate 100.

In some additional embodiments, a semiconductor device structure may be provided. For example, and with reference to FIG. 13, a semiconductor device structure 160 may include an NMOS gate dielectric 136A and a PMOS gate dielectric 136B disposed over a semiconductor substrate 102. The semiconductor device structure may also include a PMOS gate electrode structure 162 disposed over the PMOS gate dielectric 136B, the PMOS gate electrode structure 162 including a first work function metal 140 disposed over the PMOS gate dielectric 136B and a second work function metal disposed 150 disposed over the first work function metal 140. The semiconductor device structure 160 may also include an NMOS gate electrode 164 disposed over the NMOS gate dielectric 136A, the NMOS gate electrode 164 comprising the second work function metal 150.

In some embodiments of the device structure 160, the first work function metal 140 may comprise a niobium nitride having a thickness of between approximately 1 nm and approximately 5 nm. In some embodiments, the niobium nitride may comprise one of niobium nitride (NbN) or a niobium titanium nitride.

In some embodiments of the device structure 160, the second work function metal 150 may comprise at least one of a transition metal aluminide and a transition metal carbide. In some embodiment wherein the second work function metal 150 comprises a transition metal aluminide the transition metal aluminide may comprise at least one of titanium aluminide (TiAl), zirconium aluminide (ZrAl), tungsten aluminide (WAl), tantalum aluminide (TaAl), and hafnium aluminide (HfAl). In some embodiment wherein the second work function metal 150 comprises a transition metal carbide, the transition metal carbide may comprise at least one of tantalum carbide (TaC), titanium carbide (TiC), titanium-aluminum carbide (TiAlC) and a niobium-aluminum carbide (NbAlC), wherein the second work function metal may have a thickness of approximately 1 nm to approximately 5 nm.

In some embodiments of the device structure 160, the PMOS gate electrode 162 may be disposed directly over the PMOS gate dielectric 136B. In some embodiments of device structure 160, the first work function metal 140 may be disposed directly over the PMOS gate dielectric 136B. In other embodiments, the PMOS gate electrode 162 may comprise a second work function metal 150 being disposed directly over the first work function metal 140. In yet further embodiments, the NMOS gate electrode 164 may be disposed directly over the NMOS gate dielectric 136A. In additional embodiments, additional layers may be disposed between the PMOS gate dielectric 136B and the PMOS gate electrode 162, for example, in some embodiments a thin layer of titanium nitride may be disposed between the PMOS gate dielectric 136B and the PMOS gate electrode 162. In further additional embodiments, further interface layers may be disposed between the semiconductor substrate and both the PMOS gate dielectric 136B and the NMOS gate dielectric 136A.

The example embodiments of the disclosure described above do not limit the scope of the invention, since these embodiments are merely examples of the embodiments of the invention, which is defined by the appended claims and their legal equivalents. Any equivalent embodiments are intended to be within the scope of this invention. Indeed, various modifications of the disclosure, in addition to those shown and described herein, such as alternative useful combination of the elements described, may become apparent to those skilled in the art from the description. Such modifications and embodiments are also intended to fall within the scope of the appended claims. 

What is claimed is:
 1. A method for forming a semiconductor device comprising; forming an NMOS gate dielectric and a PMOS gate dielectric over a semiconductor substrate; forming a first work function metal over the NMOS gate dielectric and over the PMOS gate dielectric; and forming a second work function metal over the NMOS gate dielectric and over the PMOS gate dielectric.
 2. The method of claim 1, further comprising removing the first work function metal over the NMOS gate dielectric.
 3. The method of claim 1, wherein the first work function metal comprises a niobium nitride.
 4. The method of claim 3, wherein the niobium nitride comprises a niobium titanium nitride.
 5. The method of claim 2, wherein removing the first work function metal over the NMOS gate dielectric further comprises: selectively etching the first work function metal.
 6. The method of claim 1, wherein the second work function metal comprises at least one of a transition metal carbide and a transition metal aluminide.
 7. The method of claim 6, wherein the second work function metal comprises a transition metal carbide selected from the group consisting of tantalum carbide (TaC), titanium carbide (TiC), titanium-aluminum carbide (TiAlC), and niobium-aluminum carbide (NbAlC).
 8. The method of claim 6, wherein the second work function metal comprises a transition metal aluminide selected from the group consisting of: titanium aluminide (TiAl), zirconium aluminide (ZrAl), tungsten aluminide (WAl), tantalum aluminide (TaAl), and hafnium aluminide (HfAl).
 9. A method for forming a CMOS semiconductor device comprising; forming an NMOS gate dielectric and a PMOS gate dielectric over a semiconductor substrate; depositing by atomic layer deposition a niobium nitride layer over the NMOS gate dielectric and over the PMOS gate dielectric; etching the niobium nitride layer over the NMOS gate dielectric; and depositing by atomic layer deposition at least one of a transition metal aluminide and a transition metal carbide over the NMOS gate dielectric and over the PMOS gate dielectric.
 10. The method of claim 9, wherein the niobium nitride layer comprises a niobium titanium nitride.
 11. The method of claim 9, wherein the transition metal aluminide comprises at least one of: titanium aluminide (TiAl), zirconium aluminide (ZrAl), tungsten aluminide (WAl), tantalum aluminide (TaAl), and hafnium aluminide (HfAl).
 12. The method of claim 9, wherein the transition metal carbide comprises at least one of: tantalum carbide (TaC), titanium carbide (TiC), titanium-aluminum carbide (TiAlC), and niobium-aluminum carbide (NbAlC).
 13. The method of claim 9, wherein etching the niobium nitride layer further comprises, selectively etching the niobium nitride layer.
 14. A semiconductor device structure comprising; an NMOS gate dielectric and a PMOS gate dielectric disposed over a semiconductor substrate; a PMOS gate electrode disposed over the PMOS gate dielectric, the PMOS gate electrode comprising: a first work function metal disposed over the PMOS gate dielectric; and a second work function metal disposed over the first work function metal; and an NMOS gate electrode disposed over the NMOS gate dielectric, the NMOS gate dielectric comprising the second work function metal.
 15. The semiconductor device structure of claim 14, wherein the first work function metal comprises a niobium nitride.
 16. The semiconductor device structure of claim 15, wherein the niobium nitride comprises a niobium titanium nitride.
 17. The semiconductor device structure of claim 14, wherein the second work function metal comprises at least one of a transition metal aluminide and a transition metal carbide.
 18. The semiconductor device structure of claim 17, wherein the transition metal carbide comprises at least one of: tantalum carbide (TaC), titanium carbide (TiC), a titanium-aluminum carbide (TiAlC), and a niobium-aluminum carbide (NbAlC).
 19. The semiconductor structure of claim 17, wherein the transition metal aluminide comprises at least one of: titanium aluminide (TiAl), zirconium aluminide (ZrAl), tungsten aluminide (WAl), tantalum aluminide (TaAl), and hafnium aluminide (HfAl)
 20. The semiconductor device structure of claim 14, wherein the second work function metal is disposed directly over the first work function metal. 